1. Field of the Invention
The present invention pertains to power assemblies for raising and lowering elevators. Specifically, it pertains to a hydraulic power assembly for supplying hydraulic power to the piston and cylinder unit of a hydraulic elevator.
2. Description of the Prior Art
In a hydraulic elevator, a vertical hole is normally drilled at the bottom of the elevator shaft and a hydraulic piston and cylinder unit placed therein. A rod acting as a piston is disposed in the cylinder and attached at the upper end thereof to the base of the elevator car. When fluid power is supplied to the piston and cylinder unit, the piston rod is raised, causing the elevator to rise. To lower the elevator, fluid is simply removed from the piston and cylinder unit, allowing the piston rod to descend as the elevator car descends.
As a rule, the power assembly for supplying pressurized fluid to the piston and cylinder unit, is mounted at some accessible location and connected to the piston and cylinder unit by a hydraulic line. The power assembly conventionally includes a fluid reservoir, a hydraulic pump, and a hydraulic valve for controlling fluid flow to and from the piston and cylinder unit. In addition, control apparatus is provided for controlling the operation of the pump and control valve. These items are conventionally mounted in a unitary housing so that the power assembly can be preassembled before installation to provide a compact and easily installed unit.
Unless the fluid reservoir of a power assembly is mounted above the pump, the pump will not have a positive suction head. Therefore, in power assemblies of recent years, the pump is mounted below the fluid reservoir. As a natural consequence, the control valve is also normally mounted with the pump below the fluid reservoir. However, the control valve of a power assembly is one of the most frequently maintained components of the assembly and requires occasional removal for replacement of seals or other repairs. In power assemblies of the prior art where the valve is mounted below the fluid reservoir, removal or dismantling of the control valve frequently results in the loss of fluid and spillage on the floor. Such spillage creates unsightly as well as potentially dangerous conditions.
Power assemblies for hydraulic elevators are usually placed in restricted space areas. This also creates problems with power assemblies of the prior art. It is difficult for a repairman to work on the pump or control valve of a power assembly which is mounted in a confined space below the fluid reservoir. Not only is the space restricted, the repairman must work in a sitting or squatting position. Furthermore, the pump is frequently driven by an electric motor connected to the pump by a belt. In power assemblies of the prior art, the belt is mounted near the access to the unit where the repairman is most likely to get his hand, foot or clothing caught therein.